The most common reason for this is that you have a subtotal in your Comprehensive Income Statement (CI) which isn't found in your Statement of Changes in Equity (SOCIE), and this causes a calculation inconsistency.
Below you will find a short description of the issue and why it's happening. If you want to know how to solve the issue, we've made a step-by-step guide on how to identify and correct the issue, which you can find here.
An Explanation of the Issue
If you have state in your “Comprehensive Income Statement” that you calculate your “comprehensive income” as a sum of “net profit” and “other comprehensive income”, but then at the same time state that you calculate your “comprehensive income” as a sum of “net profit”, “exchange differences” and “cashflow hedges” in your Statement of Changes in Equity (SOCIE). This means your calculation is different from CI to SOCIE as you leave out the “Other comprehensive income” subtotal in SOCIE and this will cause a calculation inconsistency.
iXBRL is intelligent enough to know that “Comprehensive income” can be calculated in different ways in different sections of your report, but the way iXBRL is integrated means that if you report “Other comprehensive income” in CI, you need to report it in SOCIE as well.
This also means that if you have reported the “Comprehensive income” as a total in SOCIE for the “Retained earnings” column for instance, you have in effect also reported it in the CI, but then the “Other comprehensive income” subtotal is missing in SOCIE and your CI section states that “Comprehensive income” is a sum of "net profit" and “Other comprehensive income” so your calculation fails.
The only current solution (besides disregarding the calculation inconsistencies) is to keep a consistent calculation flow throughout your report and add the “Other comprehensive income” subtotal in SOCIE.